1. Field of the Invention
This invention relates to injecting a micellar dispersion into a subterranean formation and displacing it toward a production means in fluid communication with the formation to recover crude oil therethrough.
2. Description of the Prior Art
Micellar dispersions are useful for recovering crude oil from subterranean reservoirs, e.g. U.S. Pat. Nos. 3,254,714; 3,275,075; 3,506,070; 3,497,006; 3,613,786; 3,734,185; 3,740,343; 3,827,496; and other patents defining surfactant systems and assigned to Esso Production Research Company, Shell Oil Company, and Union Oil Company, etc. The micellar dispersion can be water-external or oil-external. The prior art generally teaches that the micellar dispersion is injected into the oil-bearing formation followed by a mobility control buffer and these displaced by a water drive. The micellar dispersion is displaced toward a production means from which crude oil is recovered. In general, the above patents teach that surfactant useful in the micellar dispersion can be petroleum sulfonate obtained from gas oils; or other fraction of crude oil. Much of the prior art relating to sulfonation to produce petroleum sulfonates describes processes wherein the petroleum sulfonate produced is a by-product of the polishing of lubricating stock. Different processes are needed to produce the different types of petroleum sulfonates needed for widespread effective and economic oil recovery. Processes such as those in copending U.S. Pat. Ser. Nos. 513,692, now U.S. Pat. No. 3,912,327, 376,657 teach processes wherein whole or topped crude oil are sulfonated to obtain sulfonates useful in crude oil recovery. The micellar dispersions using these new types of petroleum sulfonates contain cosurfactants. In the processes of our applications, whole or topped crude is sulfonated with sulfur trioxide and the sulfonic acids neutralized with a monovalent base to obtain the desired sulfonate, and unreacted hydrocarbon can be removed either before or after neutralization.
The prior art generally teaches that improved oil recoveries are obtained where the petroleum sulfonate is present in concentrations above the CMC (critical micelle concentration) level. Also, the prior art teaches that in order to obtain good oil recoveries with sulfonates obtained from gas oils, the sulfonate concentration should be present in concentrations of at least 4% (this concentration level can include unreacted vehicle oil within the petroleum sulfonate; thus, the concentration of --SO.sub.3 NH.sub.4 groups within a micellar dispersion can be considerably less than 1 wt. %). For example, U.S. Pat. No. 3,734,185 teaches that the minimum, ammonium petroleum sulfonate within the micellar dispersion can be 2.4% (this equals about 0.6 weight percent of --SO.sub.3 NH.sub.4 groups). In general, the prior art teaches that the sulfonate groups within the micellar dispersion can be less than 0.5 and more likely less than 0.25 for diluted surfactant systems.